A biosensor, in which a biomaterial is used as a tracing device and which has excellent sensitivity and reaction specificity, is expected to be applied to various fields, such as medical/pharmaceutical fields (clinical chemical assay and remedy), and process and environmental monitoring and chemical stability evaluation in the bio-industry. Particularly, a chemical composition assay in vivo is medically very important, and recently, the biosensor has been frequently used to assay a biomaterial sample containing blood in a medical diagnosis field. Of various biosensors, a biosensor, which employs an enzyme assay method using a characteristic reaction of an enzyme to a matrix or of an enzyme to an inhibitor, is most frequently used in hospitals and clinical chemical assays because ease of application is assured, measurement sensitivity is excellent, and the results are rapidly obtained. The enzyme assay method, which is applied to the biosensor, may be classified into an optical method, in which light transmittance is measured through a spectroscopic assay before and after an enzyme reaction, and an electrode method, in which an electrochemical signal is measured. Compared to the electrode method, the optical method is difficult to use assay of critical biomaterial because the measuring time is long, a great amount of blood is required, and measurement error occurs due to turbidity of a biomaterial sample. Accordingly, recently, the electrode method has been frequently applied to a biosensor using an enzyme. In the electrode method, after an electrode system is formed on a plastic film, an assay reagent is applied to an electrode, a sample is introduced, and specific components of the sample are quantitatively measured using a predetermined electric potential.
U.S. Pat. Nos. 5,120,420, 5,395,504, 5,437,999, and 5,997,817 are patent literatures of a biosensor, which disclose embodied operations and effects of the biosensor in detail. The disclosures of the above patents are incorporated herein by reference as follows.
FIG. 1 illustrates the production of a strip using a conventional optical method. Holes 104 are formed through a substrate 102 to allow light to penetrate therethrough, and a membrane 106, to which a biochemical reaction reagent is applied, is attached thereto. Subsequently, the resulting structure is cut into strips 108.
In the method, since the strips must be produced in a handy size, the strips are formed so as to be a few cm long. Hence, the size of a production device increases and the device costs a great deal. Since the strip is typically provided in a roll form, the substrate 102 is made of a flexible material. Accordingly, a process error occurs in the course of forming the holes by punching or of forming the strips by cutting, and thus, the uniformity of measurements is undesirably reduced. Furthermore, there is a limit that only one reaction element can be produced using one strip.
FIG. 2 illustrates the production of a biosensor strip using a conventional electrochemical method. FIG. 3 is a sectional view of the biosensor strip of FIG. 2. For convenience of understanding, thicknesses of layers are exaggerated in FIG. 3. After an operation electrode 204, a standard electrode 206, and an auxiliary electrode (not shown), on which a redox reaction occurs, are formed on an insulator 202, an insulator 210, which is processed in a predetermined shape to form a capillary 208 for feeding a sample therethrough and which acts as a spacer, is attached to the resulting insulator 202. Subsequently, a biochemical reagent 212 is applied to the electrodes, and an insulator 214 is attached thereto to form a cover, thereby completing the biosensor, in which the biochemical reagent 212 is contained in the capillary 208, through the electrochemical method. Finally, the resulting structure is cut into strips 216.
As in the production of the strips using the conventional optical method, the strips must be produced in a handy size, thus the strips are formed so as to be a few cm long. Since the electrodes must be formed on every strip, it is difficult to implement the production in a roll form, and thus, the production is typically carried out in a sheet form. When the production is conducted in the sheet manner, it is necessary to carefully handle the entire surface of a sheet because each strip is large. To produce the strips having uniform performance using a wide sheet, it is necessary to take a care in the formation of the electrodes. Additionally, since application of a solution must be conducted throughout the wide area, it is difficult to assure uniformity during a drying process. Therefore, a production device is large and costly, it is difficult to implement the production, and the production cost is high. The insulator 202 is made of a relatively thin plastic material so as to be cut into strips. When using glass or silicon wafer, the material cost of the substrate increases per strip, thus the price of the strip increases. As well, there is a limit that only one reaction element can be produced using one strip. Furthermore, a capillary having one structure can be formed in one process. If capillaries having two structures are formed, the production cost doubles.